Regulator for electric motors.



G. H. WHITTINGHAM & W. T. HOLMES.

REGULATOR FOR ELECTRIC MOTORSYF APPLICATION FILED MAYI. 19H.

1,262,290. Patented Apr. 9,191s..

2 5HEETS-SHEET l- G. H. WHITTINGHAM & W. T. HOLMES.

REGULATOR FOR ELECTRIC MOTORS.

APPLICATION FILED MAYl. I917.

1,262,290. Patented Apr. 9, 1918.

2 SHEETS-SHEET 2.

UNITED STATES PATENT OFFICE.

GEORGE H. WHITTINGI-IAM AN D WILLIAM: T. HQLMEQ, OF BALTIMORE, MARYLAND, ASSIGNORS TO MONITOR CONTROLLER COMPANY OF BALTIMORE CITY, OF BALTI- MORE, MARYLAND, A CORPORATION OF MARYLAND.

. REGULATOR FOR ELECTRIC MOTORS.

Specification of Letters Patent.

Patented Apr. 9, 1918.

Application filed. May 1, 1917. Serial No. 165,734.

To all whom it may concern Be it known that we, Gnonen H. VVHIT- TINGHAM and WILLIAM T. HoLMns, citizens Of the United States,-residinv at Baltimore, in the State of Maryland, have invented cer tain new and useful Improvements in Regulatorsfor Electric Motors, of which the following is a specification.

This invention relates to controllers for electric motors used for driving individual machines, such as certain types of printing presses, which, owing to inertia, require the development of a strong starting torque on the part of the motor, and which also require such a wide range of running speeds that in order to obtain the lowest running speed, a resistance greater than the normal starting resistance is required in the armature circuit for running. A motor of suitable size or operating such a machine at all running speeds will not develop the necessary torque for starting the load promptly if armature resistance in excess of the starting resistance is included in circuit with'the motor initially, but this excess resistance may be added after the load has been started. In the patent to G. H. lVhittingham, No. 1,2et3,665, dated October 16, 1917, is shown a controller of this kind in which the resistance, additional to the starting resistance, is normally short-circuited by a switch which is controlled by the armature circuit so as to open the switch when the current falls to a pre-determined quantity. It is desirable for some purposes, in starting the motor with its load, to be able to exclude the additional resistance and operate the motor with all of the startingresistance in circuitfor arbitrarily determined periods of time, instead of having the additional resistance included in the circuit automatically when the current falls to a pre-determined amount. The present invention therefore comprises means whereby the operator may, upon the depression of a push button switch, cause the motor to start with the full starting resistance in circuit and the additional resistance excluded, and, as long as said push button switch is closed, the full starting resistance will remain in series with the motor armature. When the motor, in the opinion of the operator, has accelerated its load to the desired degree, the said starting switch is released by theoperator and thereupon a.

greater or less amount of the entire resistance is retainedin circuit with the armature, according to the pre-set position of the speed regulating member.

The invention is applicable to either direct current or alternating current motors, and in the latter type of motor the resistances may, of course, be either ohmic or inductive.

In the accompanying drawing,

Figure 1 is a diagrammatic illustration of the invention as applied to the control of direct current motors; and,

Fig. 2 is a. similar view, showing the application of the invention to a polyphase alternating current motor.

Referring to Fig. 1 of the drawing, L and L indicate the supply wires, and S indicae a switch for connecting the supply wires to the motor controlling circuits. The direct current motor to be controlled is indicated at A, and comprises the armature a and a field winding 7. The armature circuit ex tends from contact 1 of the switch S, through conductor 2 to the fixed contact 3 of a main switch M thence through the movable arm l of said switch and conductor 5 to the armature; thence through conductor 6 to the resistance r and r of the starting and regulating rheostat R, and thence by conductors 7 and S to the contact 9 of the supply circuit switch S. The rheostat R comprises a suitable amount of resistance r, for normal starting purposes, embraced between the contacts 10 and 11, and an additional. resistance 1 in series therewith, embraced between the contacts 11 and 12. A normally open shunt circuit is provided around the part 1 of the resistance, this shunt circuit extending from the contact 11 by conductor 13 to the arm 14 of a torque switch T, thence to stationary contact 15 of said switch, and by conductor 16 to the conductor 8, which leads from the terminal 9 of the supply switch to the contact 12 f the resistance. The cou se of the armature current when the main switch M is closed and the torque switch T is open, is from contact 1 of 1711 supply switch through conductor 2 and main switch M and conductors 5 and 6, through the resistances r and 7* in series, and thence by conductor 8 to the supply switch contact 9; when the torque switch T is closed, the current will take the same course to the contact 11 oi the resist ance and will then proceed through conductor 13, switch T and conductor 16 to the supply switch contact 9, the section 1" of the resistance being thus cut out.

The torque switch T is controlled by an electro-magnet 17, the circuit 18 of which extends from the conductor 2 through a normally open push button switch 0 to the conductor l6, and when said push button switch is closed, the magnet 17 is energized and a contact surface 19 on the end of the arm 14 engages the contact 15 and closes the shunt around the section 1 of the armature resist ance. The switch T remains closed only so long as the push button switch 0 remains closed. VJ hen the operator removes his finger from said push button switch, the switch arm 14 rocks to open position by gravity, interrupting the shunt around the section 7* of the armature resistance. When the torque switch is closed, it also establishes a circuit through the coils of a magnet 20, which controls the main switch M. This circuit extends from conductor 2 through conductor 21 to a switch contact 22, thence through an insulated contact piece 23 on the switch arm 14 to a contact 24, thence through conductor 25 to the magnet 20 of the main switch, thence through conductor 26 to a normally closed push button switch C, and thence through conductor 27 to conductor 8 and contact 9 of the supply switch S. The.

switch arm 4 of the main switch M has a contact 28 thereon for engaging the contact 3, and it also has a contact 29 for engaging a stationary contact 30, and when the contacts are in engagement, the circuit of the magnet 20 is completed directly from the conductor 2 through the contacts 3 and 28, arm 4, contacts 29 and 30, and conductor 31 to the conductor 25, thence through the coils of said magnet, conductor 26, push button switch C, and conductors 27 and 28 to the supply switch contact 9. Thus, upon the closing of the torque switch T, a temporary circuit is established through the magnet 20, and the latter attracts the arm 4, closing the permanent circuit through said magnet which remains closed, even after the torque switch T opens, or so long as the magnet 20 is energized. ,When it is desired to release the main switch to stop the motor, the circuit through the magnet 20 is interrupted by depressing the push button switch C, which is the stop push button switch of the system. When the main switch is closed, it makes up another circuit which extends to an automatic device J, which operates to connect the regulating arm 32 of the rheostat E into the armature circuit, this regulating arm being normally excluded from said circuit. The device J is shown in the form of an automatic starter having a high resistance operating coil 33, and the circuit for said coil, which is made up by the closing of the main switch, extends from conductor 2, through contacts 3, 28, 29, 30, and conduct r 31 to av conductor 34, which leads to a switch t which is closed when the arm 14 of thetorque switch is in open position; but the switch t is open when the torque switch T is closed. From the switch 26, the circuit for themagnet 33 extends by conductor 35, and thence by conductor 36 to conductors 27 and 8, and thence to contact 9 of the supply circuit switch. The torque switch arm 14 is pivoted at 37 and has a short extension 14 extending below its pivotal point which'opcrates the switch 2?. This extensioniis provided with an insulated contact plate 38 with which the contact point 39 on conductor 34, and the contact point 40 on the conductor 35 engage when the torque switch is in open position, a shown in the drawing;

"l Vhen the coil 33 of the device J is energized, the contact plate 41 is moved upward,

into engagement with the movable contact devices 42, 43, and 44, in succession. These movable contact devices are connected to different points in an auxiliary resistance 1' When the plate 41 engages the first contact 42, the controlling arm or regulating arm 32 is thereby connected into the armature circuit. As shown, the conductor 6, leadingfrom the armature, connects through the resistance r with the arm 32, and thence by conductor 45 to the plate 41, thence through movable contact 42 to the resistance T and thence by conductors 46 and 8 to the con tact 9. Thus, the resistance r is placed in series with the resistance to the left of the arm 32 and in parallel with the resistance at the right of the arm 32. The movement of the starter J is suitably retarded, in the usual manner, and as the plate 41 moves upward, engaging the contacts 43 and 44 in succession, the steps of the resistance r are successively cut out of circuit so that the course of the armature current during normal operation of the motor will be from the armature through conductor 6 and that portion of the resistance at the left of the regulating arm 32, through said arm, and conductor 45, plate 41, and conductor 46 to conductor 8 and contact 9. That portion of the resistance in the regulator to the right of the arm 32 will be shunted through the circuit just traced, the amount of resistance thus shunted and the amount remaining in the armature'circuit depending upon the position of the arm 32.

The operation of the controlling device illustrated in F 1 is as follows: The operator adjusts the controller arm 32 to give the desired running speed. The supply circuit s itch S being closed, to start the motor the operator depresses the start push button switch O, thereby completing the circuit through the coils of the magnet 17 of the torque switch, and the arm 14 of the switch is attracted by the magnet and the contact 19 of said switch is brought into engagement with the contact 15, thereby shunting the part 1" of the armature resistance, but leaving the part 9, which is the normal starting resistance, in series with the armature. Simultaneously with the closure of the torqueswitch, a circuit is temporari y made through the coils of the magnet 2O 01" the main switch M by the bridging of the contacts 22 and 2a, through the insulated con tact strip 23 on the arm 14- ot the torque switch. This temporary circuit extends from contact 1 of the supply switch, through conductors 2, 21, 25. 26, 2'7, and 8, to contact 9 of the supply circuit switch. The magnet 20 attracts the arm l of the main switch and closes the armature circuit at tne contacts 3 and 28, and also closes a permanent circuit through the coils of the magnet 20. This permanent circuit extends from conductor 2, through contacts 3 and 28, and contacts 29 and 30 on the main switch to conductor thence through the coils of magnet 20, and by way of conductors 26, 27, and S to contact 9 of the supply circuit switch. The torque switch remains closed as long as the operator holds the start push button 0 depressed and said switch opens as soon as the operator releases the start push button, but the main switch remains closed after the opening or the torque switch. The armature circuit, when the main switch is first closed, extends from conductor 2, through said switch to conductor 5, thence through the motor armature to conductor 6,'and thence through the part 'r of the armature resistance, which part is the normal starting resistance, thence through conductor 13 and the torque switch to conductor 16. and thence to the contact 9 of the supply circuit switch. The circuit 'hrough the coil 33 of the device J is open at the switch when the torque switch is closed, and the switch 2. is closed when the torque switch is open. When the main switch M closes, following the closure of the torque switch, the circuit of the coil 33 of the device J is closed at the contacts 29 and 30, but it is open at the switch 2/. Hence, no current can pass through said circuit so long as the start push button 0 is depressed and the torque switch T is closed. The circuit ot the coil of the device J extends from conductor through the main switch to conductor and thence to switch t, (which is open when the torque switch T is closed) thence through conductor 35, coil 33, and thence through conductors 36, 27,

and 8, to the supply switch contact 9. It will be evident from this that so long as the operator holds the start push button switch 0 in closed position, the torque switch T will remain closed and the circuit of the coil 33 on the device J will remain open, while the main switch will remain closed. Current will flow through the armature and all of the starting resistance 1*. hen the motor with its load has accelerated as much as the operator thinks necessary or desirable, he releases the push button switch 0 and thereby interrupts the circuit through the magnet 17 ot the torque switch and the arm of said switch moves to open position, thereby breaking the shunt around the additional resistance r, interrupting the temporary circuit for the magnet of the main switch, and closing the switch 25, which completes the circuit through the coil of the device J. Thereupon, the plate l-l of said device moved at once into engagement with the contact 42 and the regulating arm 32 is connected intothe armature circuit. The armature current then divides at the point on the armature resistance 'which is engaged by said arm 32, part of the current flowing through the resistance at the right of said arm to conductors 7 and 8, and part flowing through said arm and the resistance r to conductors at and S. The device J gradually cuts out the resistance r and all of the resistance in the rheostat R which is at the right of the arm is thereby shunted. The motor will then run at a speed determined by the position of the arm 32. Thus, it the arm 32 is set in the position shown in full lines in the drawing, the motor will run at a speed below the normal, with a part of the starting resistance r in series with its ar1na ture; but it the arm 32 had been set at the point indicated by dotted lines, then the motor would run at a slow speed, with all of the starting resistance and a part of the resistance i" in series with the armature. To run at the slowest speed, the arm is moved on to the contact 12, and to run at the highest or normal speed, the arm is moved on to the contact 10.

The main purpose of the resistance r is to protect the armature in case the operator should depress and immediately release the start push button while the arm 32- is upon the first contact 10 of the armature resist ance. The depression of the start push button, as before stated, results in the closure of the armature circuit through all of the starting resistance and the torque switch; but the immediate release of the start push button would result in the opening of the torque switch and the closure of the switch t. and the contact arm 32 would then be immediately included in the armature circuit by the device J. This, in the assumed po sition of the arm 32 on the contact 10, would leave the armature unprotected it it were not for the resistance r which is included in the armature circuit at the instant when the arm 32 is included in said circuit. This re s stance r is then cut out gradually. Of course, as the regulator is designed foroperating generally at speeds below the normal, the regulator arm would be, as a rule, set to include more or less of the resistance r and r at the moment when said arm is con nected inthe circuit and thereafter while the motor is running.

In order to stop the motor, the operator depresses the stop push button C, which interrupts the circuit of the magnet 20 of the main switch, and the said switch opens, therebybreaking the motor circuits as well as the circuit through the coil of the device J, thus restoring the parts to their normal positions.

In Fig. 2 of the drawing, which represents the application of the invention to a three-phase alternating current motor, 50 and 51 represent respectively, stator and ro-- tor windings of the motor B. The start and stop push buttons are represented by O and C, respectively, the torque switch 1s 1nd1- cated at T, the main switch at M, the rheostat at R, and J indicates a device for connecting the regulating arms of the rheostat in circuit with the rotor windings. The contacts 52, 53, and 54, represent contactsof the switch for connecting the motor c1rcu1ts with the supply circuits, the switch not being shown in the drawing, and 55, 56, and 57, indicate conductors carrying the three-phase current leading from said switch to the controlling devices and motor. As shown, the conductor 55 is connected by conductor 55 to the stator windings, and the conductors 56 and 57 lead to fixed contacts 58 and 59, respectively, on the main switch M. The movable arms 60 and 61 of said switch are connected by conductors 56 and 57 to' the stator windings so that when the main switch is closed it completes the circuits from the stator windings to the contacts of the supply cir uit switch.

The windings of the rotor are connected by conductors 62, 63, and 64 to the contacts 10, 10, and 10, of the resistance in the rheostat It, which is divided into three sections, 65, 66, and 67, as shown. The contacts 12, 12 and 12, of said sections are joined together by a conductor 68 and a conductor 68. The several sections of resistance comprise parts between the contacts 10 and 11, 10 and 11 and 10 and 11 which represent the normal starting resistance, and parts between the contacts 11 and 12 11 and 12 and 11 and 12, which are in addition to the starting resistance for low speed regulation. This additional resistance is short-circuited at the time of starting by the torque switch, which is controlled by the start push button 0. As shown, the contact 11 of the resistance section 65 is connected by conductor 69 to a stationary contact 7 O of the torque switch, and the contact 11 of the resistance section 66 is connected by conductor 71 to a fixed contact 72 of said 11 and 12, contacts 11 and 12, and be- Y tween contacts 11 and 12, will be shunted through the torque switch. The torque switch is normally held in open position by gravity, or by a suitable spring, and it is moved to closed position by a magnet 17*, controlled by the start push button 0. The circuit for the coils of the magnet 17 eX- tends from conductor 55, through conductor 76 to the magnet, thence by conductor 77 to the push button switch 0, thence by conductor 78 to the conductor 57. Hence, it will be evident that the closure of the push button switch will cause the magnet 17 to be energized and attract the arm 79, which, through the insulated connections 80, will move the switch arms 74 and to closed positions and short-circuit the excess resistance in the rheostat. The arm 79 is connected by conductor 81 to conductor 78, and when said arm is attracted by the magnet 17 it engages a rocking arm 82 of a switch t and completes a temporary circuit through the coils of the magnet 20 of the main switch M. This temporary circuit proceeds from conductor 57, through conductors 78 and 81 to arm 7 9, thence to rocking arm 82, thence by conductor 83 to the coils of magnet 20, thence by conductor 85 to the normally closed push button switch C, and thence by conductor 86 to conductor 55. Hence, the closure of the torque switch completes a circuit through the main switch magnet coils from conductor 57 to conductor 55, carrying different phases of the current. As soon as the magnet 20 is energlzed, it causes the switch arms 60 and 61 to engage the contacts 58 and 59, respectively, and thereby complete the circuits of the stator windings, as before described. Simultaneously with the closure of the main switch, a permanent circuit is established through the coils of the magnet 20 by the engagement of the contact arm 61 with a contact point 87, connected to conductor 83. This contact arm 61 thus connects the stationary contact 59 with the contact 87 and the permanent circuit of the magnet 2O then extends from conductor 57, through said arm 61 and said contacts to conductor 83, thence through the coils of ihe magnet 20 and conductor 85 to the stop push button C, and thence by conductor 86 to conductor 55.

The contact arms 32 32 and 32, of the rheostat are normally excluded from the circuits of the rotor windings, and they are included upon the; closure of the switching device J, whichis controlledby a magnet 33 The-circuit of this magnet is normally open anddoes not'becomeclosed until after the torque switch and the main switch have closed and the, torque switch has again opened by reason of the release of thestart push button, The circuit of the magnet 33 extends from conductor 55, through wire 88, to. the coils of the magnet, thence by conductor 89 to the stationary contact 90,-of the switch 23, thence through the rocking arm 82 of said switch and conductor 83 to the contact 87, and, when the main switch is closed, through the switch arm 61- and contact 59 to conductor 57. The circuit of the magnet33? is therefore. normally broken at the main switch although not broken at the switch t; but upon the closure of the torque switch the circuit of themagnet 83 is interrupted at the switch t and madeiu at the main switch immediately thereafter, but itlis never closed at both points until after the main switch closesand the torque switch has been allowed to open by the release of thestart push button. I

The device J, as shown in the drawing, comprises two switch arms 91 and 92, which are electrically connected by a conductor 93 to; a segmental contact-piece 94 on the rheostat, The, arm 91 is adapted to; engagea stationary contactpiece 95, which is connected by conductor 96' to a segmental contact-piece 97. on the rheostat, and the switch arm92 is adapted to engage a stationary contact 98,-which is connected by conductor 99 to, segmental contact-piece 100-on the rheostat. The regulatingarms 32 32 and 32 are secured to a suitable insulating hub 101, one hundred and twenty degrees apart, and each contact arm, as shown, engages one of the segmental contact-pieces and the con tact of a resistance section The arms are adjusted simultaneously to corresponding points on the adjacent resistance sections. When the switching device J closes, it will be seen that the three segmental contactpieces 94:, 97, and 100, will be connected together through said device and the conductors 93, 96, and 99, and that through the regulating arms corresponding points onthe resistance sections will be electrically joined together. Thus, when the switch members of the device J are closed, those parts of the, several resistance sections between the contacts on which, said arms rest and the contacts12 12 and 12 will be short-circuited through the device J, while those parts of; the resistance sections between the con acts on hich t e ula ing ms rest andltheacontacts 10 ,;10 ,-an;d-10, will be included in: he c rcuits; 1 f. the rot of e motor,

Inpeme nmsaa he. met n-iheta t par n o is 1@e:esa m ,lli igiziilgt the magnet of the torque switch and closing the latter, causin -the excess resistance, be.- twecn contacts li -and 12?,between contacts 11" and 12 and betweencontacts ll and 12 o be bridged or short-.circuited through the torque switch, and. the remainder of the resistance to be included in the circuits of the rotor for starting purposes. Immediately following the closure ofthe torque switch, the main switch closes, and the motor startsinto operation with only the necessary starting resistance included in the circuit. of the rotor. Tl e. operatorholdsthe start push button down as long as necessary to permit the motor to start its load and accelerate as, much as isdcsirable, and he then lifts his finger from the push button switch, which causes the magnet. of the torqucswitch to be deenergized. The torque switch then opens, and this would have the elfect-of including all of the resistance in the rotor circuits, .but simultaneously with the. opening or" the torque switch, the magnet of the device J is energized and said device connects the regulating arms of the rheostat. together, and that part of the resistance between the contacts 10 10 and 10, and the regulatin arms is retained-in circuit with the rotor while: the rest of. the resistance is excluded. The parts retained will vary according-to the pre-set position of the regulating arms and the running speed will be determined by the amount of resistance included in the circuit. When the operatorrdesires to stop the motor, he presses 100 the normally closed start push button C, which interruptsthe circuit of the. magnet of the main switch, and said latter switch opens, breaking the stator circuits and also interrupting the circuits of the magnet of 1 the, switching device J. The switch-arms of the latter then move to open position, interrupting the circuits through the arms 32,

32 and 32- of the controller. The return of the switching devices to their normal posi- 110 tions includes all of the resistance in the rotor circuits.

If thespeed regulating member on the rheostat is set for a low speed, as, for instance, in the dotted line position shown in 115 Fig. 1, it would ordinarilybe undesirable to hold the starting switch O'closed long enough to .permit the motor to acquire a much higher speed than that at which it is desired to run. Therefore, the. push button 120 O, in starting, would bedepressed for a rela tively short space of time. But, if the speed regulating member were pre-set for a higher speed, as in the position indicated in full lines, Fig. 1, then the.start push button 125 would be depressed-- for a longer period of time, permitting the. motor to attain practically the speed at which it is desired to run before releasing the start switch.

In the: application ofsthe invention to 139 slip-ring induction motors, the starting resistance necessary for maximum starting torque will, of course, vary according to the characteristics of the motor, and may be greater or less than the regulating resistance.

\Vhat we claim is:

1. The combination with an electric motor, an armature circuit therefor including a starting resistance and an additional resistance and a main switch for closing the motor circuits, of a speed regulating mem ber, adjustable at will, for varying the resistance in said circuit, saidrmember being normally excluded from said circuit, a

torque switch adapted, when closed, to cut.

out the additional resistance, a manually operable switch and means controlled thereby for closing and opening the torque switch at will, and means for connecting said regulating member into the armature circuit upon the opening of the torque switch.

2. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from said circuit, a normally open torque switch for shunting said additional resistance, a normally open main switch for closing the motor circuits, manually controlled means for closing and releasing the torque switch, means for automatically closing the main switch upon the closure of the torque switch, and means for automatically connecting said regulating member into the armature circuit upon the opening of the torque switch.

3. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from said circuit, a normally open torque switch for shunting said additional resistance, a normally open main switch for closing the motor circuits, manually controlled means for closing and releasing the torque switch, means for automatically closing the main switch upon the closure of the torque switch, and means actuated by the closure of the main switch and the opening of the torque switch for connecting said regulating member into the armature crcuit.

4. The combination with an electric motor and an; armature circuit therefor including a starting resistance and an additional re sistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from said circuit, a normally open torque switch for shunting said additional resistance, a normally open main switch for closing the motor circuits, manually controlled means for closing and releasing the torque switch, means controlled by the torque switch for closing the main switch, and means for automatically connecting said regulating member into the armature circuit upon the opening of the torque switch.

5. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from said circuit, a normally'open torque switch for shunting said additional resistance, a normally open -nain switch for closing the motor circuits, a magnet for closing the torque switch, a normally open starting switch for closing the circuit of said magnet, means controlled by the torque switch, upon the closure thereof, for closing the main switch, and means for connecting said regulating members into the armature circuit when the torque switch opens.

6. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from said circuit, a normally open torque switch for shunting said additional resistance, a normally open main switch for closing the motor circuits, a normally open push button switch, and means actuated by the closure thereof for closing, first, the torque switch, and then the main switch, and means for connecting said regulating member into the armature circuit upon the opening of said push button switch.

7. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resist ance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from the armature circuit, a torque switch for cutting out said additional resistance, means for closing and opening said torque switch at will, a main switch and means controlled by the torque switch for closing the same to start the motor, and means controlled by the closure of the main switch and the opening of the torque switch for connecting said speed regulating member into the armature circuit.

8. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally 6X1 cluded from the armature circuit, a torque switch for cutting out sa d additional resistance, means for closing and opening sa d torque switch at will, a main switch and means controlled by the torque switch for closing the same to start the motor, means controlled by the closure of the main switch and the opening of the torque switch for connecting said speed regulating member into the armature circuit, and means for opening the main switch at will to stop the motor.

9. The combination with an electric motor and an armature circuit therefor including a starting resistance and an additional resistance, of a speed regulating member, adjustable at will, for varying the resistance in said circuit, said member being normally excluded from the armature circuit, a normally open torque switch for shunting said additional resistance, a magnet for closing said torque switch, a c1rcu1t for said magnet, a

normally open push button switch for closing the latter circuit, a normally open main switch, a. magnet for closing said main switch, acircuit for the latter magnet ineluding a normally closed push button switch, means for closing the circuit of the main switch magnet after the torque switch has closed, and means for connecting said speed regulating member into the armature circuit after the main switch has closed and the torque switch has opened.

In testimony whereof we have afiixed our signatures.

GEORGE H. lVI-IITTINGHAM.

lVILLIAM T. HOLMES.

Copies 0! this patent may be obtained for five cents each, by addressing the Commissioner 0! I'atents. Washington, I). G. 

